This invention relates to stand-by generators, in particular, to a relay for a transfer mechanism which transfers the supply of power between a utility source and a stand-by generator.
As is known, virtually all facilities which utilize electric power receive such power from a utility company. Typically, such utility companies have an excellent record of providing uninterrupted or infrequently interrupted power at proper voltage levels and line frequency. However, due to the increasing demands for electricity, power outages have become more frequent. While such outages usually last for a only a short duration, an extended power outage may cause more than simple aggravation for customers of the utility company. By way of example, for a residential customer, any power outage renders a home owner""s sump pump inoperable. If a power outage occurs during a rain storm, it is quite possible that the failure of the sump pump to operate will result in the flooding of a home owner""s basement.
In order to overcome these occasional disruptions in service, various customers, including home owners, have equipped their facilities with stand-by power systems. These stand-by power systems include internal combustion engines which drive electrical generators. If the commercial power from the utility company fails, the internal combustion engine is automatically started causing the electrical generator to generate power. When the power generated by the generator reaches the voltage and frequency desired by the customer, a manually operated transfer switch transfers the load imposed by the customer from the commercial power lines to the generator.
Typically, the transfer mechanism incorporates a switch which isolates the power supplied by the utility company and the generator. In a residential application, a home owner manually flips a switch between the utility source and the generator in order to provide power to the electrical system of the home. However, due to a potential time delay before the home owner can flip the switch, a significant amount of damage may be sustained by a home owner before power is supplied to the electrical system of the home. For example, an extended power outage may result in foodstuffs spoiling within a refrigerator or melting within a freezer. Therefore, it is highly desirable to provide a transfer mechanism which automatically transfers power from the utility company to the generator whenever the generator is activated.
Further, prior art transfer mechanisms require a home owner to transfer the entire electrical system of the home onto the generator. Such an arrangement does not allow a home owner the ability to decide which circuits of a home""s electrical system to be powered. As such, it is also desirable to provide a transfer mechanism which allows various branch circuits of a home to be brought on line separately, rather than at once, to allow for loads with large starting requirements to be brought up to speed before bringing the other circuit branches of the home on line thereby insuring that adequate power is provided by the generator to start such loads.
It can be appreciated that, in operation, in order to transfer power between the utility company and the generator, significant voltage and current flow through the transfer mechanism during such transfer. As such, the components of the transfer mechanism must be able to perform in such an environment without failure. As is known, the transfer mechanism must operate when exposed to high current and/or heat. Therefore, it is highly desirable to provide components for a transfer mechanism which minimize the potential for failure of the transfer mechanism when the transfer mechanism is exposed to significant current and/or heat during operation thereof.
Therefore, it is a primary object and feature of the present invention to provide for a transfer mechanism which transfers the power supplied to a load between a utility source and a stand-by generator.
It is a further object and feature of the present invention to provide a relay for a transfer mechanism which automatically transfers the power supplied to a load from the utility source to the generator in response to a power outage.
It is a still further object and feature of the present invention to provide a relay for a transfer mechanism which transfers the power supplied to a load between a utility source and a generator such that the transfer mechanism is less prone to failure than prior transfer mechanisms.
It s a still further object and feature of the present invention to provide a relay for a transfer mechanism which is reliable and inexpensive to manufacture.
In accordance with the present invention, a relay is provided relaying electrical power between first and second terminals thereof. The relay includes a stationary contact having a backing portion operatively connected to the first terminal and formed from a first material. The stationary contact also includes a contacting portion deposited on the backing portion and formed from a second material. A movable arm has a first end operatively connected to the second terminal and a second opposite end. The relay includes a movable contact having a backing portion operatively connected to the second end of the movable arm and formed from the first material. A contacting portion is deposited on the backing portion of the movable contact and is formed from the second material. A coil is operatively connected to the movable arm such that the movable arm is movable between a first contacting position wherein the contacting portion of the movable contact engages the contacting portion of the stationary contact and a second non-contacting position wherein the contacting portion of the movable contact is disengaged from the contacting portion of the stationary contact in response to an electrical charge on the coil.
A biasing structure is provided for urging the movable arm towards the non-contacting position. It is contemplated that first material be copper and the second material be tungsten. The first surface of the backing portion of the stationary contact has a first diameter and the second surface of the backing portion of the stationary contact has a second diameter which is greater than the first diameter. In addition, the first surface of the contacting portion of the movable contact has a first diameter and the second surface of the contacting portion of the movable contact has a second diameter which is greater than the first diameter. The first surface of the contacting portion of the movable contact is generally arcuate in shape and terminates at a crown.
In accordance with a still further aspect of the present invention, a contact for a relay is provided. The relay relays electrical power between first and second terminals thereof. The contact includes a backing portion formed from copper and a contacting portion deposited on the backing portion. The contacting portion is formed from tungsten.
The contacting portion of the contact includes a first surface and a second surface which engages the backing portion of the contact. The first and second surfaces of the contacting portion are spaced from each other by an outer edge. The first surface of the contacting portion has a first diameter and the second surface of the contacting portion has a second diameter which is greater than the first diameter. The first surface of the contacting portion is generally arcuate in shape and terminates at a crown. The backing portion includes a first surface which engages the contacting portion and a second surface spaced from the first surface of the backing portion by an outer edge. A mounting head depends from the second surface of the backing portion to facilitate mounting of the contact to an element.